In an electrostatic coating system, a negative high voltage is applied to a spray to provide a negative electrode and a coating objective article is grounded to provide a positive electrode, and an electric field is formed therebetween. A coating material is sprayed to the coating objective article after it is negatively charged. Recently, in the field of the electrostatic coating, water-based coating material is increasingly used. When a water-based coating material is used in an electrostatic coating system, a voltage block device is disposed between a coating material source and a spray in order to prevent the voltage applied to the coating material in the spray from passing through the conductive water-based coating material to the coating material source.
Japanese Unexamined Patent Publication (Kokai) No. 6-198228 discloses an example of the voltage block device. However, the voltage block device disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-198228 comprises separately provided first and second transfer units and a switching valve. The disclosed device is very large and therefore requires large footprint for install the device in a paint shop and an increased production cost.